1. Field of the Invention
The present invention relates to a laser video projector, and more particularly, to a laser video projector using a laser as a light source and for modulating light from the light source by an acousto-optic modulator (AOM) according to a video signal and projecting video information to a screen using a scanner.
2. Description of the Related Art
A flat panel display device such as a liquid crystal display or a cathode ray tube of a television set is a conventional representative video display means. However, the cathode ray tube or the liquid crystal display is more difficult to manufacture and the resolution becomes worse as the screen becomes larger. Accordingly, there are limits on the practical use of the cathode ray tube or the liquid crystal display the screen size of which becomes larger. Therefore, a method of enlarging an image displayed on the cathode ray tube or the liquid crystal display by a lens and projecting the enlarged image to a screen is used to realize a large screen.
A method of projecting red, green, and blue images to the screen one above the other using three cathode ray tubes and three lenses independently is disclosed in U.S. Pat. No. 4,942,525 and a method of composing images having the respective colors from the three cathode ray tubes and projecting the composed image to the screen by a lens is disclosed in U.S. Pat. No. 4,842,394.
The conventional video displaying method in the cathode ray tube or the liquid crystal display, used for displaying an image on a large screen has problems in that the picture projected to the screen is not clear since the displayed image is projected after being enlarged by the lens only and that the brightness is low since the output of the light source is limited since the video displaying means, in particular, an optical system can be damaged due to a temperature characteristic.
Also, spectral luminous efficacy of eyes varies according to the wavelengths of light. Namely, green light looks far brighter than red light or blue light in light having the same output. Therefore, when the spectral luminous efficacy of the eyes is not considered in the laser video projector which can form a large picture having high brightness and high resolution, the picture focused on a screen comes to have a color having poor contrast. Accordingly, it may not be possible to obtain a picture having high brightness and high resolution.
To solve the above problem, it is an object of the present invention to provide a laser video projector for projecting an image having high contrast and high brightness in which the color of the image focused on the screen is close to a natural color to a large screen considering the spectral luminous sensitivity of eyes according to the wavelengths of light.
Accordingly, to achieve the above object, there is provided a video projector comprising, a light source for outputting a beam of white light formed of first, second, and third main wavelengths, light separating means for separating the beam of the white light into beams of monochromatic lights having first, second, and third main wavelengths in a predetermined transmission factor and a predetermined reflectivity, light modulating means for modulating the beams of the monochromatic lights according to a chrominance signal, light combining means for combining the monochromatic lights modulated by the light modulating means into a beam, and light scanning means for scanning the combined beam of the modulated monochromatic lights, thus forming an image.
In the present invention, the light separating means preferably comprises a first dichroic mirror for reflecting at least 99% of monochromatic light having a first wavelength from the beam of the white light and transmitting at least 95% of monochromatic light having second and third wavelengths, a second dichroic mirror for reflecting at least 99% of monochromatic light having the second wavelength and transmitting at least 95% of monochromatic light having the third wavelength, and a high reflection mirror for reflecting at least 99% of the monochromatic light having the third wavelength.
Also, in the present invention, wherein the light modulating means preferably comprises three acousto-optic modulators for modulating the beams of the monochromatic lights having the first, second, and third wavelengths. The light combining means preferably comprises a third dichroic mirror for transmitting the beam of the monochromatic light having the first wavelength and reflecting the beam of the monochromatic light having the second and third wavelengths, a fourth dichroic mirror for reflecting the monochromatic light having the second wavelength and transmitting the monochromatic light having the third wavelength, and a high reflection mirror for reflecting the monochromatic light having the third wavelength.